(1) Field of the Invention
The invention relates to reference generating circuits. Specifically, a circuit for providing start-up power to current mirror based reference generator.
(2) Background
Modern computer systems and electronic devices frequently include circuits that require a start-up power source in order to either “kick” a circuit out of a zero current state or to hasten the circuit's power-up process. Faster start-up of key circuits like oscillators and power conversion circuits decreases the wait time for a user upon starting a device or waking the device from a low power state.
Computer systems and electronic devices have increasingly been designed for portability including the advent of such devices as laptop computers, handheld computers, Personal Digital Assistants (PDAs) and similar devices that rely on batteries for a significant part of their power. Therefore, it has become increasingly important that start-up circuits also minimize the amount of power consumed during the start up sequence and afterward by minimizing power consumption or inefficiencies caused by the extra circuitry required to implement the start-up circuit.
When batteries are inserted or other power sources are first connected to a device, components such as oscillators require a reliable initial voltage or current to be supplied to the component in order to ensure that the component can successfully transition from a zero-current state to a steady state of operation. Further, the kick-start circuit must not subsequently attempt to provide a kick-start to a circuit that has reached its steady state because this would be likely to cause erratic behavior in an important component. For example, if an oscillator received a kick-start while in normal operation an unreliable clock signal might result which would destabilize the entire system.
Current start-up systems require excess circuitry in order to accomplish the task of preparing a system for normal operation. Many systems like oscillator circuits produce unreliable or spurious output during the start-up phase. This requires circuits that rely on the output of oscillation circuits to have additional circuitry to filter out the initial unreliable signals. This is often accomplished by waiting or ‘counting’ for a period of time after start-up until it is known that a required component will have successfully started and will provide a reliable signal. This requires extra circuitry to implement, consumes additional power and involves a significant delay. Circuits that kick-start a circuit by supplying an initial bias to the circuit often include circuitry to sense the state of the circuit to be biased and to shut off that bias when the circuit reaches a certain threshold. Implementing this wait or counting operation requires extra circuitry in order to detect the state of a circuit and to cut off the bias source from that circuit. This extra circuitry consumes additional power that shortens the life span of a battery or similar power supply.